1. Field of the Invention
The present invention relates to electronic indicators, more particularly, to an electronic indicator that has a spindle displacement to measurement display ratio that can be set by the user.
2. The Prior Art
A mechanical dial indicator uses a longitudinally reciprocating rod, or spindle, to measure a length or distance, typically lengths that are not more than 3 or 4 inches, and to display that length on a dial face. In older dial indicators, the longitudinal motion of the spindle is translated to rotational motion for display on the dial face through the use of a rack and pinion. The teeth of the pinion mesh with and are driven by the teeth of the rack on the spindle, causing the pinion to rotate in response to the longitudinal movement of the spindle. The rotational motion of the pinion is transferred, via other gears, to a rotating dial hand. The dial hand indicates, via markings on the dial face, the distance that the spindle has traveled longitudinally relative to the pinion.
Since the late 1970's, electronic indicators have been developed. In the electronic indicator, the movement of the spindle is translated into an electronic signal representing the spindle displacement. That signal is either displayed, via a numerical display, on the face of the indicator, or is outputted via a connector for input to another instrument, or both.
Some uses of indicators require that measurements be taken where the variations between the work piece and spindle are not 1:1, due to unusual part configuration. Such applications include chamfer gauges, inside diameter/outside diameter gauges, fixture gauges where it is not possible to mount the indicator at a normal 9020 the part due to space constraints, and gauges involving lever-type motion transfer mechanisms. For example, a lever-type motion transfer mechanism may have the lever pivot nearer to the spindle end so that for every 3 mm displacement at the measuring end of the lever, the spindle end is only displaced by 2 mm. It would then be desirable to have an indicator that reads a 3 mm displacement for every 2 mm of actual displacement of the spindle so that the user does not have to perform the translation mentally or with a calculator.
One parameter that has been carried over from the mechanical dial indicator is the fixed ratio of the spindle displacement to the displayed or outputted value. The assumed ratio is 1:1. The display ratio is set at the factory and cannot be changed by the user. When a ratio other than 1:1 is implemented, for example the 3:2 ratio in the above example, the phrase `Special Ratio` or an equivalent is typically added to the dial indicator to insure that the user knows that the readout responds to something other than 1:1 in reference to spindle movement. Consequently, users need a variety of electronic indicators if they need a variety of displacement-to-display ratios, at least one indicator for each ratio.